Divide the dough into 12 equal portions, using a scale for accuracy if available; mine weighed about 2 ounces each. Roll each portion into a smooth ball and place on a parchment-lined baking sheet about 2 inches apart. Cover with a clean kitchen towel and let rise another hour. Heat oven to 350°F and arrange rack in the middle.
Using a 2-inch glass or jar (something that is smaller than the kolaches, I used an espresso tamper) press down on each circle to create an indentation in the middle of each. Press firmly, the dough should be almost transparent on the bottom. If the glass is sticking dip it in flour. Beat the remaining egg with a little water and brush the egg wash all over each kolache.
Spoon 1 tablespoon of the poppy seed filling into each round then sprinkle with the streusel.
Bake for 20 minutes or until golden brown and firm on the outside.
While the kolaches bake, mix the 1/4 cup powdered sugar and 1 teaspoon lemon juice in a small bowl until smooth.
Remove kolaches from oven and set baking sheet on a wire rack. Drizzle with the glaze.
Serve warm for breakfast with coffee or tea. Any leftover kolache can be kept covered in the refrigerator for up to 3 days. Rewarm before serving.